The present invention relates to a dot formation method in an ink-jet image-forming method, that is, a dot formation method at the time of making prints by using a printer of an ink-jet system, and also concerns an image-forming apparatus for forming images in accordance with such a method.
In image-forming apparatuses of the ink-jet system (hereinafter, referred to as ink-jet printers), various studies have been made on improvements of the dot formation method in order to improve the image quality and to shorten the drying time.
For example, Japanese Laid-Open Patent Application No. 330086/1993 xe2x80x9cTokukaihei 5-330086 (published on Dec. 14, 1993)xe2x80x9d (U.S. Pat No. 5,596,355) discloses a technique in which an image-forming process is carried out by using a slow-drying black ink that has high reproducibility in black color although it takes a long drying time and a quick-drying black ink that has only a thin printing density although it has a short drying time. In this technique, in the case when a color dot is formed adjacent to an area in which black dots are formed, the border area is formed by using the quick-drying black ink or superposing inks of CMY on each other, and the other areas are formed by using the slow-drying black ink.
This arrangement has achieved an improvement of the reproducibility in black color, and has made it possible to reduce bleeding occurring on the border between black dots and color dots.
Moreover, Japanese Laid-Open Patent Application No. 149036/1995 xe2x80x9cTokukaihei 7-149036 (published on Jun. 13, 1995)xe2x80x9d discloses a technique in which black ink having low permeability to recording paper and CMY ink having high permeability thereto are used. FIGS. 29 and 30 disclose an example of dot formation using this technique. More specifically, in the case when a color dot area is formed adjacent to an area in which black dots are to be formed, the black dots within the black dot area are thinned, and instead of these, color dots are formed. Moreover, this example also shows that color dots are formed as a base of a black dot area so that black dots are superposed on the color dots.
This arrangement prevents bleeding occurring on the border between a black dot area and a color dot area, and also shortens the drying time of the black dots. Moreover, Japanese Laid-Open Patent Application No. 197831/1996 xe2x80x9cTokukaihei 8-197831 (published on Aug. 6, 1996)xe2x80x9d also discloses a similar technique.
Moreover, Japanese Laid-Open Patent Application No. 336961/1996 xe2x80x9cTokukaihei 8-336961 (published on Dec. 24, 1996)xe2x80x9d discloses a technique in which dots in a solid portion are thinned so as to shorten the drying time. This example also discloses a technique in which, upon thinning dots in the solid portion, the outline is printed as it is without thinning dots so as to prevent a shaggy printing (burr appearance) from spreading at the outline portion.
Here, in a separate manner from the above-mentioned improvements in the printing methods, many techniques have been proposed so as to shorten the drying time of printed objects by installing a drying means such as a heating device using a halogen lamp.
However, the following problem is caused by the technique disclosed in the above-mentioned Laid-Open Patent Application No. 330086/1993, upon forming an area having a great back dot density (hereinafter, referred to as a solid black area).
Since the solid black area is formed by using black ink of a slow-drying type having high black reproducibility in order to improve image quality, insufficiently dried black ink causes stains, set-off, etc. on the printed object. This is because there is a correlation between the black dot density and the drying time, with the result that a solid black area that has a high dot density and that also has an area exceeding a certain extent, for example, characters having not less than 10 point or lines and dots having not less than 0.5 point, needs a long drying time.
In particular, in an ink-jet printer using the facedown system in order to improve the operability, there are problems in which ink adheres to a transport roller, etc. that first comes into contact with the printed face immediately after the printing process and re-transferring of ink to the recording paper.
In contrast, in the case when black ink of a quick-drying type is used to form the solid black area, its poor reproducibility causes degradation in the image quality.
Moreover, in the techniques disclosed in Japanese Laid-Open Patent Applications No. 149036/1995 and No. 197831/1996, besides the above-mentioned problems, another problem arises in which a color dot, that is, a monocolor of yellow (Y), magenta (M) or cyan (C), mixedly exists in the border area within the black dot area, thereby causing degradation in the image quality of black color.
Furthermore, with respect to a method for shortening the drying time in the case when the black dot density is high, no method has been disclosed.
In the technique disclosed in Japanese Laid-Open Patent Applications No. 336961/1996 (Tokukaihei 8-336961), the thinning process of black dots causes problems of a reduction in the density and degradation in the image quality.
As described above, in the above-mentioned conventional techniques, those problems arise due to the fact that no consideration is given to the drying time of the solid black area in the image formation.
In the technique using a drying means, in addition to the necessity of a complicated apparatus construction, another problem arises in which there is an increase in the power consumption due to power to be consumed in the drying means.
The objective of the present invention is to provide an image-forming method and an image-forming apparatus of an ink-jet system which can omit the installation of, or reduce the scale of a drying means that has high power consumption and causes high costs of the apparatus, and which can also dry an area with high dot density while reducing degradation in the image quality.
In order to achieve the above-mentioned objective, an ink-jet image-forming method of an ink-jet system in accordance with the present invention in which dots are formed by using a slow-drying ink having a comparatively long drying time and a quick-drying ink having a comparatively short drying time so that the dots form an image is provided with an arrangement in which: the density of the dots in an image area within a predetermined range is discriminated based upon image data, and based upon the results of the discrimination, selection is made between slow-drying ink and quick-drying ink so as to form the dots.
In the above-mentioned method, upon forming the dots, the density of the dots in an image area within a predetermined range is discriminated based upon image data. Based upon the results of the discrimination, either the slow-drying ink or the quick-drying ink is selected, or both of them are selected, and the dots are formed by using the selected ink.
In general, the drying time of ink forming dots is influenced by the density of the dots at a position in which the dot is formed. Thus, as the drying time becomes longer, the above-mentioned problems arise. In contrast, when the quick-drying ink is used, it is possible to shorten the drying time. However, since the quick-drying ink generally has a low printing density and low color reproducibility, the application of only the quick-drying ink tends to cause degradation in the image quality of an printed image.
Here, in the above-mentioned method, the density of the dots is discriminated, and based upon the results of the discrimination, a judgment is made as to whether or not the period of the drying time raises any problem. Then, in accordance with the judgment, selection is made from the slow-drying ink and the quick-drying ink so as to form the dot; thus, it is possible to shorten the ink drying time and also to reduce degradation in the image.
In other words, the density of the dots is discriminated, and in the case when the results show that the period of the drying time raises any problem, ink is selected in a manner so as to use the quick-drying ink more; thus, it is possible to shorten the ink drying time. In contrast, in the case when the judgment shows that the period of the drying time raises no problem, ink is selected in such a manner that only the slow-drying ink is used or the slow-drying ink is used more; thus, it is possible to reduce degradation in the image quality of an image as a whole. Consequently, the above-mentioned method makes it possible to avoid an increase in the drying time, that is, a reduction in the printing speed, while maintaining high image quality by reducing degradation in the image quality of a printed image.
Moreover, in order to achieve the above-mentioned objective, the ink-jet image-forming apparatus of an ink-jet system of the present invention in which dot are formed by using a slow-drying ink having a comparatively long drying time and a quick-drying ink having a comparatively short drying time so that the dot form an image is provided with a calculation means which, upon forming the dot, calculates a dot area rate that represents the density of the dot formed within a predetermined area for the dots, and a discrimination means which, based upon the dot area rate, selects ink to be used from the slow-drying ink and the quick-drying ink.
In the above-mentioned arrangement, the dot area rate is calculated by the calculation method. Then, based upon the dot area rate, the discrimination means selects ink to be used for forming the dots from the slow-drying ink and the quick-drying ink.
Thus, the above-mentioned image-forming method can be carried out, and the following effects can be obtained. Consequently, a drying device, etc. used for shortening the drying time can be omitted, or the scale thereof can be reduced. In other words, while eliminating the necessity of delaying the printing speed or installing a device for drying the printed object in order to dry ink and the subsequent increase in the output, high image quality can be maintained. Therefore, it is possible to provide an inexpensive, small-size ink-jet image-forming apparatus which can achieve high image quality, high printing speeds, a simple apparatus structure and small power consumption.
Moreover, in the image-forming method and the image-forming apparatus of an ink-jet system of the present invention, the image areas are set in association with respective dots at the time of image formation, and the dot area rate representing the density of dots, formed in each image area, is calculated, and when the image area in question is a group of high-density dots that is a set of dots corresponding to the image areas in which the dot area rate becomes greater than a predetermined value, the slow-drying ink is superposed on the quick-drying ink so as to make printing.
In the above-mentioned method and arrangement, since the quick-drying ink forms the base of the slow-drying ink, it is possible to further improve the permeability of the slow-drying ink into recording paper, and consequently to further shorten the drying time of the ink. As a result, it is possible to avoid a reduction in the printing speed while maintaining high quality of an image to be formed.
Additionally, none of the above-mentioned conventional techniques disclose an arrangement in which, the image area in question has a dot area rate greater than a predetermined value, the slow-drying ink is superposed on the quick-drying ink so as to make printing.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.